Preheat oven to 350°F (175°C). Lightly grease a 9×13-inch baking dish.
In a large mixing bowl, combine thawed hash browns, cream of chicken soup, sour cream, melted butter, onion powder, garlic powder, salt, and pepper.
Fold in shredded cheddar cheese until well blended.
Spread mixture evenly into the prepared baking dish.
If using topping, mix crushed cornflakes or crackers with melted butter and sprinkle over the casserole.
Bake uncovered for 45–50 minutes, or until hot and bubbly and topping is golden brown.
Allow to cool slightly before serving.